This application claims the priority of Korean Patent Application No. 2002-80832, filed on Dec. 17, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a mobile electronic unit, and more particularly, to an apparatus for controlling a power source in which power consumption is minimized in a power off mode without additional hardware, in a mobile electronic unit using a variety of types of batteries that have different nominal voltages.
2. Description of the Related Art
The digital camera, which is a type of mobile electronic unit that has a fundamentally different concept than the film-based camera, has been rapidly adopted by increasing numbers of photographers. The digital camera photographs a subject through an optical lens system and stores photographed image information as digital data in a memory card. The digital data stored in the memory card can be processed in a desired shape using a computer and can be easily supplied via a network. Demand for digital cameras is expected to continue increase.
Digital cameras employ a variety of power sources, such as +3.3V, +4.5V, and −9V, according to the operational characteristics of each unit constituting the digital camera. In a digital camera, as shown in FIG. 1, a conventional apparatus for controlling a power source includes a battery unit 11, a switch unit 12, a detection unit 13, a first power source unit 14, a second power source unit 15, a control unit 16, and a camera unit 17.
Referring to FIG. 1, if the switch unit 12 is turned on, the detection unit 13 recognizes that the switch unit 12 is turned on and applies a signal to the control unit 16. The control unit 16 operates by a power source supplied from the second power source unit 15. When the camera does not operate, that is, even when the switch unit 12 is turned off, an output voltage of the battery unit 11 is applied to the control unit 16 through the first power source unit 14 such that the output of the detection unit 13 is continuously monitored. When the camera operates, the control unit 16 detects that the switch unit 12 is turned on, controls the first power source unit 14, and supplies a variety of power sources to the camera unit 17.
In such an apparatus for controlling a power source, when the output voltage of the battery unit 11 is higher than an operational voltage of the control unit 16, the second power source unit 15 is implemented with a voltage drop circuit. When the voltage drop circuit is constituted of a switching regulator, the efficiency of the power source circuit is high, but power consumption of the power source circuit is high. Thus, even when the camera does not operate, power consumption of the battery unit 11 increases. Meanwhile, when the voltage drop circuit is constituted of a series regulator, which is cheaper than a switching regulator, consumption of the battery unit 11 increases because the cost of the power source circuit is low but much heat is generated and the efficiency of the power source circuit is lowered. In addition, when the voltage drop circuit is constituted of both the switching regulator and the series regulator, the structure of the power circuit becomes complex, and costs increase. Meanwhile, when the output voltage of the battery unit 11 is lower than the operational voltage of the control unit 16, the second power source unit 15 is implemented with a voltage boost circuit or a voltage boost and drop circuit. In this case, the voltage boost circuit or the voltage boost and drop circuit can be implemented with the switching regulator. Power consumption of the power source circuit is high, the cost thereof is high, and the efficiency thereof is lowered compared to the efficiency of the voltage drop circuit.
Further, there are a variety of nominal voltages of a battery used in a digital camera such that an operational voltage of the control unit 16 corresponds to a middle range of an output voltage of the battery unit 11. In this case, when the second power source unit 15 is implemented with a series regulator, if the output voltage of the battery unit 11 is lower than a rated output voltage of the second power source unit 15, that is, the operational voltage of the control unit 16, the second power source unit 15 outputs the output voltage of the battery unit 11 without change to the control unit 16. This results in the shutdown of the control unit 16. In order to prevent this phenomenon, if the power source unit is implemented using the switching regulator for the voltage boost or drop circuit and the series regulator, the complexity of hardware increases, costs increase, and voltage conversion is performed twice, thereby causing an efficiency of the power source circuit to be lowered.